Ongoing characters offer recognition value, as the reader at the book store thinks, 'hey it's a Nero Wolfe book I haven't read,' or someone buys a ticket for 'the new Batman movie.' People tend to repeat pleasurable experiences even after a few misfires. But this has a drawback or two as well, one of which is the characters aging inconveniently as the years go by. A lot of pulp heroes had serving in the Great War as part of their backstory, which was fine in 1932 but by the end of the pulp era around 1949, it made them seem like they should be a bit past their physical prime. Then you get someone like Nick Fury or Reed Richards... having them WW II veterans in 1963 put them in their 40s, but by 1980 it was awkward having them remember being in the Battle of the Bulge.
Even James Bond, whose books only spanned a little over a decade, needed some tinkering. By the time Ian Fleming was writing the final books, Bond's history contradicted himself and either he was older than the mandatory retirement age for 00-agents or he had purchased his first Bentley when he was thirteeen.
Here is one of DC's attempts to twiddle with the ongoing problem. Say Superman was 21 when his first stories appeared in 1938. That's fine, except then stories told when he was a boy had to be set earlier than that. Superboy stories in the late 1960s featured Bonnie and Clyde, Hitler, Stalin and other denizens of the 1930s... when if readers paid attention would make the current Superman fifty years old. Now, I'd be okay with a greying Superman but Dc thought this wouldn't appeal, so this page appeared in SUPERBOY# 171, January 1971 to clarify things.
You know, this problem comes about because characters are kept current beyond normal limits. I really don't think Stan Lee expected Spider-Man to last more than four or five years; he probably figured super-heroes would be popular for awhile and then fade to be replaced by Westerns or horror titles. But no. High school student Peter Parker is still putting on his costume and climbing up the wall almost fifty years later. This had led to reboots and restarts and mass murders of entire universes in various Crises (I personally think if you lived through the Crisis on Infinite Earths and remembered it, you would be hopelessly traumatized).